What is Hypromellose?

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hypromellose for eye

Hypromellose, short form of chemical name Hydroxypropyl methyl-cellulose (HPMC), is a semi synthetic, inert, viscoelastic polymer used as a lubricant, as well as an excipient (pharma-cologically inactive substance used as a carrier for the active ingredients of a medication) and controlled-delivery component in oral medications found in variety of commercial products. The very high viscocity of hypromellose makes it ideally suited to use in ocular preparations which are designed to address dry eye. Some artificial tears contain hypromellose, and the polymer is also used in some types of eye surgeries to keep the eye lubricated. As a lubricant, it can soothe the eye in case of irritation and also create a protective barrier to protect the eye from additional irritation. This polymer is considered to be non-toxic, although it can be flammable in some settings, and is produced by many companies, some of which specialize in production for very specific applications. Products with hypromellose can be found over the counter in some regions, and are also available by prescription.

What are the general properties of Hypromellose?

Hypromellose is a solid, and is a slightly off-white to beige powder in appearance and may be formed in granules. The compound forms colloids (substance which is microscopically dispersed evenly throughout another substance) when dissolved in water. Even though non-toxic, it is combustible and can react vigorously with oxidizing agents. Hypromellose is and aqueous solution which does not show thermal gelation (thickening) property. When the solution heats up to a critical temperature, the solution congeals into a non-flow able but semi-flexible mass.


What are the Test methods for qualifying Hypromellose?

Different test methods are used to qualify Hypromelllose. They are as follows.

  • Viscosity test methods: Since hypromellose exhibits pseudo plastic properties, many test methods are available and the results of various methods and the results of viscometers do not necessarily communicate to each other. Typical viscosity test will specify solution concentration, viscometer spindle number and solution temperature.
  • Degree of substitution: This is the average level of methoxy substitution on the cellulose chain. The average value is between real number 0 and 3 The degree of substitution is often expressed in percentages.
  • Molar substitution: This is the average level of hydroxypropoxy substitution on the cellulose chain. Since hydroxypropoxy base can be attached to each other on side chains and does not require a base substitution site on the cellulose molecule, this number can be higher than 3. Molar substitution is also expressed in percentages.
  • Salt content: Content of NaCl in weight percentage of dry powder weight.
  • Moisture: Since all cellulose are hygroscopic, they will absorb moisture from surroundings if left exposed from original packaging. So, moisture must be tested and weight corrected to ensure enough amount of dry active material is aportioned for usage.


What are the uses of Hypromellose?

In addition to the use in eye medicines, they have many other uses. They are as follows.

  • Hypromellose can control the rate of drug delivery, making sure that the body is not flooded with a medication.
  • It acts as a inert thickener in oral medications which improves the texture without compromising the function of the compound in the drug.
  • Hypromellose is also used in foods to thicken, suspend or emulsify ingredients.
  • It is vegetarian, which makes it optional to gelatin in foods which are meant to be safe for vegetarians.
  • It is also used in cosmetics, paints, adhesives and some cleaning products.
  • In construction materials, the moisture retaining properties of the compound may be an added advantage, although it can also be problematic if the compound is not stored and handled properly, as it can increase in weight as it picks up water.
  • Hypromellose solutions were patented as a semi-synthetic substitute for tear-film.
  • It is also used in cement renders, Gypsum products, pharmaceuticals.

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